Localised dynactin protects growing microtubules to deliver <i>oskar</i> mRNA to the posterior cortex of the <i>Drosophila</i> oocyte.

Abstract

The localisation of <i>oskar</i> mRNA to the posterior of the <i>Drosophila</i> oocyte defines where the abdomen and germ cells form in the embryo. Kinesin 1 transports <i>oskar</i> mRNA to the oocyte posterior along a polarised microtubule cytoskeleton that grows from non-centrosomal microtubule organising centres (ncMTOCs) along the anterior/lateral cortex. Here, we show that the formation of this polarised microtubule network also requires the posterior regulation of microtubule growth. A missense mutation in the dynactin Arp1 subunit causes most <i>oskar</i> mRNA to localise in the posterior cytoplasm rather than cortically. <i>oskar</i> mRNA transport and anchoring are normal in this mutant, but the microtubules fail to reach the posterior pole. Thus, dynactin acts as an anti-catastrophe factor that extends microtubule growth posteriorly. Kinesin 1 transports dynactin to the oocyte posterior, creating a positive feedback loop that increases the length and persistence of the posterior microtubules that deliver <i>oskar</i> mRNA to the cortex.